FRANKFURT/ZURICH (Reuters) – Specialty chemicals group Clariant (CLN.S) has hired Goldman Sachs (GS.N) as an additional adviser to help stave off an activist investor’s campaign to derail its planned merger with U.S. peer Huntsman (HUN.N).

The Swiss company is facing pressure from White Tale Holdings, which holds more than 10 percent of its shares and is lobbying other investors to oppose the $20 billion merger with Huntsman.

Clariant said in May that it was working with Citi (C.N) and UBS (UBSG.S) on the planned merger, while Bank of America (BAC.N) and Moelis (MC.N) were acting as Huntsman’s financial advisers..

“We can confirm that we have retained Goldman Sachs as additional adviser in relation to the investment, the positions taken and demands made by White Tale,” a Clariant spokeswoman said on Monday.

The addition of Goldman is designed to help lobby shareholders to support the deal, people close to the matter said.

“Goldman has been taken on board because of their knowledge and ties to U.S. investors and ability to predict and preempt White Tales’ next moves,” one of the people said.

Clariant Chief Executive Hariolf Kottmann has been in discussions with White Tale and the two sides have assured each other they would continue a dialogue, the source added.

Kottmann told Reuters last week that the company’s 20 largest shareholders do not oppose the deal — with the exception of White Tale.

Next Steps Unclear

White Tale, which has said it does not believe the Huntsman deal is the best way to unlock value, has for its part so far not communicated which specific steps it may take next, people close to the matter said.

It could potentially call for an extraordinary general meeting to scupper the merger plans.

The activist has also reached out to fellow shareholders in Clariant, some of whom will meet Clariant’s senior management during a roadshow following last week’s second-quarter earnings.

“Some investors are open for other ideas,” a person familiar with White Tale’s thinking said, without being more specific.

Among others, a group of Bavarian families who hold about 14 percent in Clariant have been approached by an investor whose association with White Tale remains unclear and who tried to persuade them to oppose the Huntsman merger.

The family, however, rejected that approach in writing, a person familiar with the matter said.

“The families have committed themselves, in a legally binding way, to support the merger,” another source said.

Clariant’s shares are up about 5 percent since the announcement of the merger in May.

While it remains unclear whether a bid from a third party would emerge for Clariant if the Huntsman deal failed, some peers have evaluated their options with respect to Clariant in the past.

German peer Evonik (EVKn.DE) held talks with buyout group CVC [CVC.UL] over a potential joint offer for Clariant to then split up the company, with Evonik taking the special chemicals and CVC taking the commodities business, people familiar with the matter have said.

Evonik would look at Clariant’s specialty chemicals unit again should it come on the block, people familiar with the matter said.